1. Field of the Invention
The present invention relates to a tongs apparatus, and more particularly to a tongs apparatus capable of providing supplemental holding force.
2. Description of the Related Art
Conventionally, when a crane or a like machine is used to suspend an object, such as a piece of titanium sponge, a log, or a piece of concrete, which has a relatively soft surface layer and a cylindrical shape that is difficult to grasp, or is used to change the orientation of the object from a horizontal orientation to a vertical orientation, or vice versa, a wire, a chain, or the like is used as a holding jig in order to perform the suspending and orientation-changing operation in preparation for various machining processes.
However, in many cases an object, such as a piece of titanium sponge, which is used as an industrial material is large and heavy, and therefore skill is required in an operation of holding such a large and heavy object, in a well-balanced manner, by use of a holding jig and suspending the object by use of the crane. Therefore, a suspending method which improves work efficiency has been desired.
FIG. 5 shows a tongs apparatus 100, which is an example of a known tongs apparatus for suspending a heavy object. Generally, the tongs apparatus 100 is attached to a hook of a crane and is used to suspend an object, such as a piece of steel, aluminum, stone, or any other material.
The tongs apparatus 100 includes an engagement member 102 provided on the crane side of the apparatus 100; an engagement pin 101 which engages a hook (unillustrated) of the crane; paired cross arms 104 for holding an object; tension bars 103 rotatably connected to the cross arms 104; a frame 105 to which the cross arms 104 are rotatably connected; and a stopper 106 disposed under the frame 105 and capable of contacting the upper face of the object.
The tongs apparatus 100 is equipped with a lock mechanism consisting of a tong male key 110a and a tong female key 110b. The tong male key 100a is provided on the engagement member 102 side, and the tong female key 110b is provided on the stopper 106. The cross arms 104 of the tongs apparatus 100 are held in an opened state by the lock mechanism.
The lock mechanism is locked through an operation of lowering a crane hook in a state in which the stopper 106 is placed on an object or a frame and the cross arms 104 are opened outward. That is, when the crane hook is lowered, the tong male key 110a enters the tong female key 110b. As a result, a projection provided on the tong male key 110a rotates, and thus, the lock mechanism is brought into a locked state. In a locked state, the cross arms 104 do not close even when the tongs apparatus 100 is pulled upward by the crane.
When an object is to be suspended by use of the tongs apparatus 100, the tongs apparatus 100 in which the lock mechanism is in the locked state and the cross arms 104 are in the opened state is suspended from the crane. Subsequently, the tongs apparatus 100 is positioned above the object.
Subsequently, when the lock mechanism is unlocked, the cross arms 104 close due to their weights, so that the distal ends of the cross arms 104 come into contact with the object. The unlocking of the lock mechanism is effected through an operation of lowering the crane hook in a state in which the stopper 106 is placed on the object or the frame, so that the projection of the tong male key 110a rotates, and the tong male key 110a is released from the tong female key 110b. Thus, the lock mechanism is unlocked. When the crane hook is raised, due to the weight of the object and that of the tongs apparatus, the cross arms 104 intrude into the object, which enables holding of the object.
When the cross arms 104 are to be opened again after the object has been moved to a desired position, the crane hook is lowered such that the stopper 106 of the tongs apparatus 100 is placed on the object. When the crane hook is lowered further, the tension bars 103 and the cross arms 104 rotate about pins 108 and pins 109, respectively, such that the angles formed between the tension bars 103 and the cross arms 104 become smaller. As a result, the cross arms 104 are opened.
However, in the tongs apparatus 100 shown in FIG. 5, the stopper 106 must be placed on the object or frame in order to open or close the cross arms 104 and unlock the lock mechanism. Therefore, when the stopper 106 is placed on a cylindrical object, such as a piece of titanium sponge, whose outer diameter is not constant, and whose outer circumference is uneven, the relative positions of the distal ends of the cross arms change depending on the outer diameter of the object, so that holding a desired portion becomes difficult.
In order to solve the above-described problem, a tongs apparatus as shown in FIG. 6 has been proposed. In this tongs apparatus, cross arms are opened and closed through vertical movement of a motor-driven chain in order to hold an object at a desired position. Specifically, the tongs apparatus 100 shown in FIG. 6 has a chain motor 114 disposed on the engagement member 102 provided on the crane side. A hook 112 is provided at the lower end of a chain 111 extending from the chain motor 114. The hook 112 has a configuration that enables the hook 112 to engage a lifting pin 113a of a lifting block 113 provided on a base plate 107. When the chain 111 is wound up by the chain motor 114, the cross arms 104 open.
Further, a safety device (unillustrated) is added to the tongs apparatus 100 shown in FIG. 6 in order to protect the chain motor 114 and the chain 111. The safety device includes a limit switch or a proximity switch for detecting the fully opened state of the cross arms 104 and automatically stops the chain motor 114 when the cross arms 104 are fully opened.
When an object is suspended by use of the tongs apparatus 100 shown in FIG. 6, the engagement pin 101 is brought into engagement with the hook (unillustrated) of the crane. Subsequently, the crane is operated to lift the tongs apparatus 100 and move it to a position above the object. Subsequently, the chain motor 114 of the tongs apparatus 100 is operated in order to unwind the chain 111. As a result, due to the weights of the cross arms 104, forces act on the cross arm 104 inward or in a closing direction.
When the inner sides of the cross arms 104 come into contact with the object, the safety apparatus stops unwinding of the chain, while the chain 111 is slightly slackened. Thus, a holding position of the object is determined. Since the chain 111 is slightly slackened, due to the weights of the cross arms 104, forces further act on the cross arms 104 inward or in a closing direction. At this time, if the chain is caused to slack excessively, the chain may entangle. Therefore, the limit switch or proximity switch detects such slack and adjusts the length of the unwound portion of the chain 111 in order to prevent such excessive slack.
Subsequently, the tongs apparatus is lifted by use of the crane. At this time, due to the weights of the object and the tongs apparatus, forces further act on the cross arms 104 inward or in a closing direction. In this manner, the object is held by the cross arms 104, lifted by means of the crane, and changed in orientation.
When the tongs apparatus 100 shown in FIG. 6 lifts a hard object such as a piece of copper, aluminum, or stone, the cross arms 104 can hold and suspend the object. However, when the cross arms 104 hold an object having a soft surface layer such as titanium sponge, the unwinding of the chain 111 is stopped immediately after the cross arms 104 come into contact with the surface layer, with the result that the object cannot be held reliably.
That is, lifting of the tongs apparatus is started before the distal ends of the cross arms 104 intrude into the inner hard portion of the object. In such a case, the cross arms 104 cannot lift the object, and instead fracture the surface layer of the object.